The invention concerns a process for finish-machining the bearing star of a constant-velocity joint, especially for automobiles, with a spherical bearing surface for mounting in a bearing cage and a plurality of guide tracks that basically run axially and interrupt the spherical bearing surface for the bearings arranged in the pocket of the bearing cage that transmit the torque between the bearing casing and the bearing star.
In automobiles with front-wheel drive, the front wheels are driven by joints. Therefore, front-wheel axle shafts must have joints that allow the wheels both to spring in and out, and also to lock. Constant-velocity joints (homokinetic joints) are used to make the wheels drive as steadily as possible. Fixed constant-velocity joints designed as cap joints are used for joints on the front axle shafts, inter alia, while moving constant-velocity joints designed as cap joints are used for joints on the rear axle shafts and allow axial movement in addition to flexure of the joint.
These cap joints are comprised of a bearing star set on the wheel end of the axle shaft, on which the bearing cage with its bearings and the bearing casing connected to the wheel driveshaft sit. On a fixed constant-velocity joint, the bearing casing and the star have curved tracks on which the bearings move. On a moving constant-velocity joint, the tracks on the bearing casing and the star are designed to be even.
On the constant-velocity joints comprised of a bearing star, bearing cage and bearing casing that are known in practice, the finish-machining of the bearing casing, which has a bearing surface for mounting in a cage and guide tracks for the balls, takes a large number of different steps, which are sometimes done on different machines. Starting with a drop-forged bearing-casing blank, the known finish-machining methods produced the guide tracks by broaching and milling, while the bearing surface is produced by turning. Machining is very expensive, especially finish-machining bearing stars of fixed constant-velocity joints, because both the bearing surface and the guide tracks are designed to be curved in the axial direction of the bearing casing.
The disadvantage of this known production method is that because different machine-tooling methods are used, in which the bearing star being machined must be transformed many times and potentially fed to different machines, it is very time-consuming and hence expensive to finish-machine the bearing star. What is more, because of the various transformations, defects occur so that tolerances are only possible within certain limits.
The problem of the invention is to provide a method of finish-machining the bearing star of a constant-velocity joint so that bearing stars can be finish-machined in a simple, inexpensive way the can be fully automatated with high precision.
The invention solves this problem by producing both the spherical bearing surface for mounting in the bearing cage and the guide tracks for the bearings by a hard-rotary turning operation.
This production method in the invention makes it possible, for the first time, to make the bearing star of a constant-velocity joint by a uniform machine-tooling method, namely a turning operation method, where the turning occurs after the chucking of the blank of a bearing star. As a result of machining only by the turning operation on a machine, the method in the invention has a clear advantage in terms of time, cost and precision over the finish-machining method known in practice.
One practical embodiment of the invention proposes that the axial course of the guide tracks be designed purely spherically.
The invention also proposes that the axial course of the guide tracks be composed of a cylindrical part and a spherical part. Both sorts of bearing stars are used for fixed constant-velocity joints.
In one practical embodiment of the invention, the tangents of the balls with the accompanying guide tracks run spatially parallel to one another. In particular, the design of the spherical guide tracks also proposes that the distance between the tangents of the balls and the accompanying guide tracks change in the axial direction, which optimizes the transmission of torque.
The invention also proposes that the guide tracks can run at a sharp angle to axis of rotation of the bearing star.
One special embodiment of the invention proposes that the bearing star have a polygonal recess to connect it to the wheel driveshaft. The design of this polygonal recess for the wheel driveshaft, where the driveshaft has a corresponding polygonal contour on the outside, makes it possible to prevent any play around the bearing star/driveshaft connection, as is the case in the known state-of-the-art axial toothing.
In another advantageous embodiment of this bearing star, the polygonal recess is designed to be conical in the axial direction. This conicity of the polygonal recess permits self-centering of components being connected to one another, and no play in the bearing star/driveshaft connection in the axial and radial directions. There is also better transmission of forces, tooth effects and smaller structure.